Japanese Patent Laid-Open Publication No. 7-128983 discloses a developing device for use in an electrophotographic image forming apparatus. The developing device includes a cylindrical toner bearing member (i.e., toner roller) opposed to a photosensitive member for bearing toner particles therearound and a developer bearing member (i.e., developer roller) spaced a slight gap away from the toner bearing member for bearing a two-component developer material consisting of carrier particles as well as toner particles. According to the developing device, the toner particles supported on the developer bearing member are transferred to the toner bearing member in a transfer region where toner bearing member opposes to the developer bearing member. Then, the toner particles so transferred to the toner bearing member are supplied to the photosensitive member to develop an electrostatic latent image formed on the photosensitive member into a visualized image in a developing region where the toner bearing member opposes to the photosensitive member.
This type of developing device requires each incremental peripheral portion of the toner bearing member moving past the developing region to bear a constant amount of toner particles thereon to ensure the visualized image to have a constant density. To this end, two techniques are proposed in the art. One technique, which is illustrated in FIG. 5A, is to remove all the toner particles supported on the toner bearing member therefrom after it has moved past the developing region and then to provide the toner bearing member again with the toner particles in the transfer region where the toner bearing member confronts the developer bearing member. The other technique, which is illustrated in FIG. 5B, is to supply toner particles only to portions on the toner bearing member from which the toner particles has been transferred to the photosensitive member.
The former technique, however, requires the toner particles that have removed from the toner bearing member to be re-mixed into the two-component developer material in a space of certain volume. This results in the developing device to be larger in size and complicated in structure. Also, using a scraper to remove the toner particles from the toner bearing member will disadvantageously result in an fusing of toner particles both on the scraper and toner bearing member at which the scraper contacts with the toner bearing member and scratches on the toner bearing member by the contact with the scraper. Instead, other members such as collecting roll and brush roll are proposed to remove the toner particles from the toner bearing member, which further requires the use of the scraper for removing toner particles from the collecting roll or brush roll, also resulting in the developing device to be complicated and larger in size and the fusing of the toner.
The latter technique, on the other hand, as illustrated in FIG. 5B, the toner particles are also supplied to one portions that still bear toner particles even after the previous developing process as well as other portions that that have been deprived of toner particles therefrom in the previous developing process. This results in an unevenness of the amount of toner particles on the toner bearing member, adversely superimposing a pattern that corresponds to the previously visualized image onto the newly developed image. Also, the toner particles that have not consumed for developing can remain unused for a long period of time to be stressed by the continuous contact with the photosensitive drum, which may result in the fusing of toner on the toner bearing member.